Variable voltage divider



@G 99 m45 E. W. BssQN 29E-S6935?.

VARIABLE VOLTAGE DIVIDER Filed Oct. l5, 194.3

Hl/S Attorneg.

PatentedvOct. 9, 1945 atraen VARIABLE vooraan nrvmaa Ernest W. Bisson, Albany, N. Y.,

eral Electric Company,

York

asslgnorvto Gena corporation of New Application @otober l5, i943, Serial No. 506,397

Claims.

My invention relates to variable capacitive voltage dividers and has for its principal object the provision of a new and improved voltage divider of such type having a substantially constant total capacitance between line conductors.

Capacitive voltage dividers now commonly used comprise a pair of variablecapacitors mechanically coupled for simultaneous capacity variation in opposite senses and so arranged that when the capacity of either capacitor is a minimum the capacity of the other capacitor is a maximum. Such an arrangement provides satisfactory voltage division, but has the disadvantage that the total line to line capacitance of the divider varies from zero, or some small minimum value, to a maximum and back to zei-,o within the range of. operation. In many applications such Wide variation of line to line capacitance is undesirable, as in transmission line attenuators, or in balancing capacitors for direction' iinders and the like, or wherever it is desired to maintain the total input capacitance of the divider substantially equal to the characteristic impedance of e., prescribedtransmission line.

In accordance with my invention, the total input capacitance of a. variable capacitive voltage pair of mechanically interconnected and oppo sitely variable capacitors B and 9. A voltage of variable intensity appears upon the directly connected plates of the capacitors B and. Q and is supplied to any desired electrical load l@ through a suitable lvariable voltage lead il. in' the em@ bodiment of Fig. l, the ,capacitors o and l are physically independent. The capacitor El comprlseska stationary plate i3 and a moving plate lf3, While the capacitor 9 similarly comprises stational-y plate I 5 and a moving plate t5. The moving plates id and it are mounted at spaced points upon a common rotatable shaft indicated at il, and the stationary plates it and are so disposed with respect to the associated moving plates Ill and i5, respectively, that when the capacitance of either capacitor is a maximum, the capacitance of the other capacitor is a mmimiun or zero. In the drawing the shaft il and the plates i# and I6 are shown in the midposition ci vze divider is maintained substantially constant throughout its range of operation by connecting, in parallel with a pair of serially connec-d oppositely varying' voltage dividing capacitors, a pair of parallel connected oppositely varying capacitors having a minimum combined capaci" tance in the region of the center ci their range of capacity variation.

The nature of my inventionitseli will be more fully understood, and its objects and advantages further appreciated, by referring now to the following detailed specification taken in conjunction with the accompanying drawing, in which Fig. l is a partially schematic circuit diagram of a capacitive voltage divider embodying my :lnvention; Fig. 2 is a partially schematic circuit diagram of another embodiment of my invention; Fig. 3 is a simpliiied schematic circuit diagram ci the arrangements shown at Figs. l and Z; Figs. 449, inclusive, are graphical representations of certain of the electrical characteristics ci the circuits shown at Figs. 1, 2, and 3; and Fig. l@ is Simpliiied schematic circuit diagram or still another embodiment of my invention..

Referring now toFig. 1, I have shown a variable capacitive voltage divider comprising a pair of line conductors F:land G coupled to a source of alternating current supply l and having connected therebetween in series circuitl relation av their range oi movement.

Connected in parallel circuit relation with ,the serially connected capacitors 8 and S, l provide a pair ofparallel connected capacitors it and i9. The capacitor I8 comprises a stationary 20 and a moving plate 2l, while the capacitor it comprises a stationary plate 22 and a moving plate 23. The moving plates il and are mounted at spaced points upon a rotatable shaft 24, and the associated stationary plates 2?@ and 22 are so positioned that the capacimce of 'notie capacitrs it and H9 is a minimum, or solistenn tially zero, when the shaft 2d is in its midpcsition, the capacitance of one capacitor increasing to its maximum .as the shaft 2d is rotated to its limit of movement in one direction and the capacitance of 'the other capacitor increasing to a. maximum as the shaft 24 is rotated to the limit of its movement in the opposite direction. In the iliustrated embodiment of the invention, the il and 25 have c shown mechanicaiiy inter connected and both controlled by a suitaiile man ually operable control knob Q5. it will o?? course be understood that, ii desired, the moving plates lil, it, il, and may .all be mounted upon the same sha t.

At Fig. 2, l have shown another embodiment o my invention in which the capacitors d and have been combined into a single structural unit having a common movable plate 2S and the capacitors it and i3 combined into another structure having a common movable plate 2l. ni all other respects the arangement of Fig. Z is similar to that of Fig. 1 and like parts have been assigned the saine reference numerals. "i

have also shown, at Fig. 3, a simplied circuit diagram in which the capacitors l, 9. I8 and I9 fand the mechanical interconnections therebetween are all shown only schematically. Electrically the circuit of Fig. 3 is the same as that of` Figs. l and 2 and like parts have been assigned the same reference numerals. Y

With the foregoing understanding of the construction and arrangement of the various parts of my voltage divider, its mode of operation will now be understood by referring particularly to Figs. 3, 4, 5, and 6. At Fig. 4 the broken lines Cs and C9 illustrate, respectively, the manner of variation of the capacities of the capacitors 8 and 9 as the shaft Ii is moved from one limit of its movement to the other. Since the capacitors 8 and 9 are connected in series circuit relation, the sum of their capacities is expressed in the equation where Cs is the sum or series capacitance of the capacitors 8. and 9. The curve Cs of Fig. 4 shows the manner in which the sum or series capacity Cs varies as the shaft I1 ls moved throughout its range of movement. l

At Fig. 5, I have shown a similar diagrammatic representation oi' the manner in which the individual and sum capacities of the capacitors i8 and I9 vary as the shaft 2i is moved through its range of operation. From Fig. 5 it will be evident that the capacity Cia of the capacitor I8 decreases substantially linearly from a maximum at onelimlt of movement of the shaft 24 to .substantially zero at the midpcsition of the shaft and remains at zero as the shaft is moved from its mid position to the other limit of its range of movement. Similarly, the capacity Cie of the capacitor I9 decreases substantially linearly from a maxi- A mum at this other limit of the range of movement of shaft 24 to substantially zero as the shaft is moved back to its mid position and remains at zero for all shaft positions at which the capacity Cia is above zero. It may now be noted that the sum of the capacities of the capacitors i8 and i9 may be expressed as CP=C1B+C19 since these capacitors are connected in parallel circuit relation.v

Cp is the parallel or sum capacity of the capacitors i8 and I9 and is represented at Fig. 5 by the heavy line Cr.

The total input capacitance between. the line conductors 5 and 6 of Figs. l, 2, and 3 is the sum of the combined capacities of the capacitors 8 and 9 and the combined capacities of the capacitors I8 and I9. This input capacitance may be represented as Cr and will be seen to be equal to Cs-l-CP, where range of movement of the capacitor plates. Fig.

shown at Fig. 2, the minimum capacity of the capacitors I8 and I 9 at the center of the range of movement of the shaft 24 will usually be somewhat above zero due to the proximity of the mov-l ing plate 2'I to both the stationary plates 2li and 22. Similarly, it is very diflicult to reduce the capacitance of either of the capacitors t or 8 entirely to zero, especially where a common moving plate 26 is used as at Fig. 2. It will be understood, of course, that these conditions also prevail to a lesser extent in connection with the mechanically separate capacitors illustrated at At Fig. 7, I have shown a curve Cs' representing the sum of the capacities of the capacitors il and 9 for conditions where the limiting values of Cs' are somewhat above zero, Similarly, at Fig. 8 I have shown a curve CP' representing the sum of the capacities of the parallel connected capacitors I8 and IB where the minimum capacity at the middle of the range of operation is somewhat above zero. At Fig. 9, I have plotted the sum of the curves Cs' and Cr' to illustrate the total input capacity Cr for these conditions. It will be evident from Fig. 9 that the total input capacity Cr is more nearly constant for the practical conditions illustrated at Figs. '7, 8, and 9 than i'or the purely theoretical conditions illustrated at Figs. 4, 5, and 6.

It will of course be understood that by varying the shapes o f the capacitor plates capacity characteristics slightly different than those shown in connection with Figs. l and 2 may be obtained, and that by suitable proportioning a substantially unvarying net input capacitance may be obtained. or the net input capacitance may be caused to vary slightly in a desired manner.

At Fig. l0, I have shown a further embodiment of my invention where tio capacitive voltage dividers of the type shown in Figs. 1, 2, or 3 are connected together by means of their variable voltage leads II to form a transmission line having substantially constant input and output capacities.

trically to those of Figs. 1. 2, or '3 and that like parts have been assigned like reference numerals. The pairs of capacitors 8, il and I8, I9 of Fig. 10 may be structurally separate, as at Fig. 1, or multiple in form, as at Fig. 2. The moving elements of all the capacitors of Fig. l 0 are shown connected together and to a manually operable control member 25'.

While I have described only certain preferred embodiments of my invention by way of illustration, many further modifications will occur to those skilled in the art and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications as fail within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States, is:

M1. A variable capacitive voltage divider comprising a pair of serially connected capacitors simultaneously variable in opposite senses over a predetermined range of variation and having a maximum sum capacitance in the region c! the aesaesi center of saidl range, a second pair of capacitors connected in parallel circuit relation with each other and with said serially connected capacitors, said second pair of capacitors being simultaneously variable in opposite senses over a predetermined range of variation and having a minimum sum capacitance at the region of the center of said range, and manually operable control means interconnecting said pairs of capacitors for simultaneous variationlthroughout said ranges.

2. A variable capacitive voltage divider comprising a source of alternating current supply, a pair of variable capacitors connected in series ciru cuit relation across said source, control means for varying simultaneously and in opposite senses the capacities of said series connected capacitors from minimum to maximum over a predetermined range of opration of said control means, a second pair of capacitors connected in parallel circuit relation with respect to each other across said source, and means comprising said control means for varying simultaneously and in opposite senses the capacities of said parallel connected capacitors from maximum values at opposite limits of said range of operation to minimum values at the region of the center of said range.

3. A variable capacitive voltage divider comprising a source of alternating current supply, a pair of variable capacitors connected in series circuit relation across said source, movable control means for varying the capacities of said series capacitors in opposite senses from minimum to maximum values between the limits of 'a pre-i determined range of movement of said control means, a second pair of capacitors vconnected in parallel circuit relation with each other across said source, means connecting said control means to vary the capacity of each of said parallel convalue at one limit of said range while maintaining the capacity of the other of said parallel'connected capacitors at its minimum value, and a variable voltage load circuit connected across one of said serially connected capacitors.

4. A variable capacitive voltage divider comprising a source of alternating current supply, a first pair of variable capacitors vconnected in series circuit relation across said source of supply and having a common movable element, manually operable control means for moving said element through a predetermined range of movement to vary the capacities of said serially connected capacitors in opposite senses from maximum to minimum values between the limits of said range of movement, a second pair of variable capacitors connected in parallel circuit relation across said source and having a second common movable ele ment, and means connecting said second movable element for control by said manually operable means to vary the capacity of each of said parallel connected capacitors from a minimum value at the center o said range of movement to a maximum value at one end thereoiwhile mainm taining the capacity of the other of said parallel connected capacitors at a minimum value, Whereby the total input capacity of said voltage divider is maintained substantially constant.

5. A variable capacitive voltage divider comprising a pair of mechanically interconnected capacitors oppositely variable over their operating range and connected in series circuit relation, a second pair of mechanically interconnected capacitors oppositely variable over different portions of their operating range and connected in parm allel circuit relation, and control means intere connecting said pairs of capacitors for simultaneous capacitance variation.

ERNEST W. Bisson. 

